Index: src/Parser/parser.yy
===================================================================
--- src/Parser/parser.yy	(revision 777ed2b6fddb63be60f52f784e80cc5897a6d457)
+++ src/Parser/parser.yy	(revision 04cccaf91ae4feec9313b029eeecf652dccee9cb)
@@ -2294,8 +2294,10 @@
 		{ $$ = new ExpressionNode( new TypeExpr( maybeMoveBuildType( $1 ) ) ); }
 	| assignment_expression
+		{ SemanticError( yylloc, toString("Expression generic parameters are currently unimplemented: ", $1->build()) ); $$ = nullptr; }
 	| type_list ',' type
 		{ $$ = (ExpressionNode *)( $1->set_last( new ExpressionNode( new TypeExpr( maybeMoveBuildType( $3 ) ) ) ) ); }
 	| type_list ',' assignment_expression
-		{ $$ = (ExpressionNode *)( $1->set_last( $3 )); }
+		{ SemanticError( yylloc, toString("Expression generic parameters are currently unimplemented: ", $3->build()) ); $$ = nullptr; }
+		// { $$ = (ExpressionNode *)( $1->set_last( $3 )); }
 	;